Controlled ultraviolet spark



July 16, 1940. F. E. NULL CONTROLLED ULTRAVIOLET SPARK Filed Sept. 2,1958 WITNESSES INVENTOR .Fay' E. Vill BY m, Mr

ATTORNEYS Patented July 16, 1940 UNITED STATES PATENT OFFICE 2,208,386CONTROLLED ULTRAVIOLET SPARK Fay E. Null, Ridgefield, N. J. ApplicationSeptember 2, 1938, Serial No. 228,179

This invention relates 3 Claims.

to a device for producing ultraviolet sparks and has for an object toprovide a device where the spark or sparks may be controlled.

Another object of the invention is to produce a device wherein a highvoltage spark may be obtained with a constant intensity when over aperiod of time In the accompanying averaged longer than one second.

drawingever, the usual spark moves back and forth erratically in spaceand usually presents a zig zag irregular length path. by reason of thenoise It also is objectionable produced and is otherwise objectionableunless enclosed in a metallic housing. In the present ing terminals mayinvention two or more sparkbe used with high voltage (100,000 volts)without objectional actions on the terminals or electrodes and withoutnoise. Also,

according to the present invention a high voltage spark may be producedwhose intensity is constant when averaged over an appreciable period oftime,

ment (tungsten,

as for instance, for more than one a line spectrum of-the eleetc.) usedfor electrodes is produced with a strong, continuous background. As thecontinuous background is weak compared with the strong lines desiredintense line emission, the

the rest of the spectrum by means of a filter.

The narrow spectral range selector is sufficiently pure for manyprocesses and experiments. While the device may be used for variouspurposes, it

is particularly valuable tensity of light sources in controlling theinthat are ordinarily subject to considerable variation, such as sparksand arcs. The spark source produced by repeatedly discharging acondenser across a gap a series of very intense but very light.

consists of brief flashes of When such a light source is used forbactericidal action or as a catalyst in chemical reactions its effectdepends in general upon the average light energy leaving and does notdepend upon given out steadily or short intense flashes.

the source per second whether the light is is emitted in the form of Thedevice embodying the invention does not attempt to control the intensityof each flash but keeps the energy of the light emitted by the flashesin any .1 of a second the same iskept constant as that emitted in anyother .1 the average light intensity hen this average istaken over canreadily be separated from time intervals long relative to the durationof a single flash. One of the great advantages of keeping the averagelight intensity approximately constant lies in the fact that it may beduplicated whenever desired. Referring to the accompanying drawing, itwill be seen that wiring for securing a regulated spark of a desiredintensity has been illustrated. A part of this wiring includes acondenser and a sparking device for projecting a line of light in a Todesired direction. As indicated in the drawing, the wires l and 2 supplyalternating current from any desired source at a desired voltage, as forinstance, volts. This line voltage leads directly into a condensercharging circuit A. As- 16 sociated with this circuit are three othercircuits, namely, a timing circuit B, an input shunting circuit C and acontrol circuit D. All these circuits coact so that by adjusting thevariable resistance 3 in the control circuit D the light in- -2 tensityfrom the spark may be maintained constantly, as hereinafter fullydescribed. In order that this may be fully understood the variouscircuits will be described. From the drawing it will be seen that theline voltage impressed across the variable choke l, across the fixedchoke 5 and across the primary 6 of the transformer 1 whereby current isinduced in the secondary 8 which has its ends connected respectively toopposite sides of the condenser 9. When I the, 30 voltage in condenseris high enough it jumps the gap l0 and thereby produces a spark whichgives off an intense light. Part of the light from this spark strikesthe cell l l (which is a photosensitive cell) and generates a currentwhich passes in series through the primary I2 of a. transformer l3. Thisinduces a current in the secondary it of transformer I3 which lattercurrent passes to the A. C. amplifier l5 which is connected by twooutput transformers l6 and I1 to the timing network in the timingcircuit B. v

This network produces a D. C. voltage across the resistance l8 which isa function of the intensity of the spark for any desired number ofpreceding spark discharges. The transformers I6 and [1 are connected inseries with the rectifiers l9 and the resistances 20. 'Ihe'secondaryleads of the transformers l6 and I1 are connected opposite in phase sothat one passes current for the positive part of the amplifieroutputvoltage 50 and the other passes current for the negative part of theamplifier output voltage. Thus the current drops across resistances 20are voltages which depend at any instant upon the intensity of the lightreceived by the cell II at that instant. 55

' erasing the record These voltages across the resistances 20 causecurrents to flow charging the condensers 2| through resistances 22.During the part of a cycle during which the voltage across a rectifierI9 is negative, 2i partially discharges through the series resistances22 and 23,- thus partially of the amplifier output for the immediatelypreceding half cycle and for What remains of other preceding halfcycles. By properly adjusting the capacities and resistances, the memoryof the previous current can be integrated so that the voltages acrossthe condensers 2! depend to any desired amount upon the intensities ofprevious half cycles of the amplifier output. The sum of the voltages onthe condensers is impressed upon the rectifier l9 and the resistance 18in series.

The voltage across resistance 3 is balanced against the voltage acrossthe potentiometer or variable resistance 3 of the controlcircuit D, theresultant voltage being impressed across the grid and filament of the23, which has a high impedance input. The actuating tube 23 passes acurrent whenever the intensity of the spark exceeds a certain amountwhich is determined by the setting of the potentiometer 3. When theactuating tube (thyratron) 23 passes current a voltage is induced in thetransformer 25 which is sufiiciently large to make the actuating tube(thyratron) 26 of the circuit C conducting even though thefilament-plate voltage on tube 26 may be small at that instant. Whencurrent flows in the transformer 27 of the circuit C it acts as a shunton the transformer l of the charging circuit .A which charges thecondenser Q. This'shunting action decreases the voltage across theprimary of the transformer 7 by effectively changing the time constantof the circuit and causing the charging time of the condenser 9 to belonger. This results in fewer sparks per cycle and reduces the lightenergy emitted by the light source per second.

The actuating tube (thyratron) 23 must have a tube 23 a chance to passcurrent and actuate the transformer 25during every charging cycle of thecondenser 9. This is most conveniently accomplished by using the inputvoltage across the transformer l on the primary of the transformer Whenthis A. C. Voltage induced in the secondary of the transformer 28 isless than the voltage of battery 29,110 current carrfiow through thetransformer 28 because of the rectifier '33. If under this condition thetube 23 does not pass current, the voltage across its filament-platewill be equal to the voltage of battery 3i. Then if the filament-gridvoltage on tube 23 is now increased until it exceeds the critical value,the tube 23 Will pass current through resistance 2 3. This current willthen continue to flow regardless of any change in the filament-gridvoltage, until the voltage induced in the secondary of transformer 28minus the value of the voltage of battery 29 is greater than the currentdrop actuating tube (thyratron) filament-grid voltage is.

. variable resistance 3 the current is blocked). During the stoppage ofthe current through tube 23 a voltage is induced in transformer 25whichbreaks down the actuating tube 26, thus shunting the primary of thetransformer 1. By adjusting the relative values of the voltages acrossbattery 29 and transformer 28 it is possible to have this shuntingaction occur at any desired magnitude of the sinusoidal A. C. voltageWave across the primary of transformer l. The current throughtransformer 27 remains blocked until the magnitude of the voltage acrosstransformer 28 has fallen to such a value that the voltage of battery 3|exceeds the current drop across resistance 24. Current will now startflowing through the actuating tube 23 if the voltage impressed acrossthe filament-grid of tube 23 exceeds the critical value, and be blockedthrough transformer 28 by the rectifier 30. Thus, whenever the currentis increased or decreased through tube 23 a voltage is induced intransformer 25. By altering the connection of the secondary leads fromtransformer 25 it is possible to make the grid of tube 26 positive withrespect to its filament when the current through tube 23 is increasing(or decreasing by reversing secondary leads). Tube 26 can only passcurrent however when the plate is positive with respect to the filamentand this only occurs for the positive half of the input input voltage onthe lead-in wires i and 2, or

can be built on successive negative half'cycles 0f the input voltage onlead-in Wires i and 2, but cannot be made positive on both the positiveand negative halves of the input voltage cycle. As shown in the drawing,the source intensity can only be correct on successive half cycles ofone polarity of the input voltage.

When the voltage across variable resistance 3 in the control circuit Dis adjusted so that tube 23 passes current during a maximum part of thetime, the amplifier output meter M in the timing circuit B has a minimumreading. When the tube 23 does not pass current the reading of the meterM is a maximum. If the voltage across the is adjusted about half waybetween the two extreme conditions it maintains the average value of thereading of the meter M constant, corresponding to a certain averageintensity of light from the spark for when the transformer l is shuntedmore or less of the time to maintain the average value of lightintensity from the spark constant.

I claim:

1. In a device of the character described, a sparking device, acondenser interposed in the circuit rent from said cell for timing thefunction of said sparking device, and a circuit for controlling theintensity of the spark may be regulated. and the number of sparks in agiven time controlled.

2. In a device of the character described, a sparking device, meansincluding a source of alternating current, a transformer .and acondenser for producing a spark in said sparking device, a photoelectriccell positioned to receive light from said sparking device, a shuntinput circuit having an auxiliary transformer, said shunt circuit havingthe primary winding of the first mentioned transformer in series withthe primary Winding of the auxiliary transformer for varying theintensity of the spark, a circuit for controlling the action of thefirst mentioned transformer including the secondary Winding of saidauxiliary transformer, a variable resistance and an auxiliary circuitprovided with current from said cell, said auxiliary circuit beingprovided with means for supplying direct current to said variableresistance for holding back current passing therethrough.

3. In a device of the character described, a sparking device, a chargingcircuit including a source of current, a charging transformer, and acondenser, a photoelectric cell positioned to receive light from saidsparking device, a second circuit having a second transformer forcontrolling the voltage supplied to said charging transformer, theprimary winding of said charging and said second transformer being inparallel, an actuating tube positioned in series with the secondarywinding of said second transformer, said actuating tube and secondtransformer acting as a shunt across the charging transformer primarywhen actuated by a voltage on its gridlament, a second actuating tubefor controlling the first mentioned actuating tube, a third circuitprovided with current from said photoelectric cell and means fordirecting current from said third circuit for actuating said secondactuating tube.

FAY E. NULL.

